Town of Plymouth (Mass.) Retirement Board is moving to a manager-of-managers program to invest its $120 million in assets and is looking for a firm to run it, said Karry Barros, spokeswoman. The firm would decide which of the plans managers would be retained, although some managers cannot be terminated because of contracts, Ms. Barros said. Plymouth currently has eight external managers. She did not know if the plans investment consultant, Segal Advisors, or its custodian, State Street, would be terminated. A date for a selection has not been set.